Nowadays, wireless communication networks have experienced great growth. In addition to mobile phone networks, wireless computer networks are now rapidly gaining in popularity. The introduction of the wireless local area network (WLAN) has allowed users to freely carry computing devices within the area of the WLAN while still being connected to the network.
The original WLAN standard IEEE 802.11 was designed to enable communications at 1–2 Mbps in a band around 2.4 GHz. In order to enable higher data rates, IEEE working groups have defined the 802.11a, 802.11b and 802.11g extensions to the original standard. The 802.11a standard, for example, enhances data rates up to 54 Mbps over short distances in a 5 GHz band. Whereas, the IEEE 802.11b protocol defines data rates up to 22 Mbps in the 2.4 GHz band.
Referring to FIG. 1, a schematic circuit block diagram of a WLAN module operated according to the IEEE 802.11 a/b/g protocol is shown. The WLAN module 10 comprises an antenna switch 11, a radio-frequency integrated circuit (RFIC) 12 and a baseband/media-access-control integrated circuit (BB/MAC IC) 13. One end of the WLAN module 10 is connected to a notebook computer, and the other end thereof is connected to antennas 15 via RF connectors 14.
When the WLAN module 10 is in a receiving mode, the two antennas 15 receive RF signals over the air, and transmit the RF signals to the RFIC 12 via the antenna switch 11. Since only one antenna is used according to the IEEE 802.11a/b/g protocol, in response to a control signal from the BB/MAC IC 13, the antenna switch 11 selects the desired one having better signal quality. Then, by means of the RFIC 12, the frequency of the RF signal outputted from the antenna switch 11 is reduced from high to low. The low-frequency signal is transmitted to the BB/MAC IC 13 for demodulation. The demodulated signal is transmitted to the notebook computer. On the contrary, in a transmitting mode, data from the notebook computer is processed and modulated by the BB/MAC IC 13. The modulated signal is amplified by the RFIC 12 to have a higher frequency. The high-frequency signal is then transmitted to the air via the desired antenna 15.
As known, according to the IEEE 802.11a/b/g protocol, data transmission rate for the WLAN communication can reach 54 Mbps. Nowadays, IEEE working groups have designed the IEEE 802.11 TGn protocol to enable communications up to 100 Mbps. The IEEE 802.11 TGn protocol is applicable to a multiple-input multiple-output (MIMO) technology. Referring to FIG. 2, a schematic circuit block diagram of a MIMO system is shown. At least two, e.g. three, antennas 15 are employed to receive RF signals in the same band. Each antenna 15 is electrically connected to a RFIC 12 via a RF connector 14. In a receiving mode, the RF signals received from the antennas 15 are reduced by the individual RFIC 12 from high frequency to low frequency. The low-frequency signal is transmitted to the BB/MAC IC 13 for demodulation. The demodulated signals are synchronously transmitted to the notebook computer. Whereas, in a transmitting mode, data from the notebook computer is processed and modulated by the BB/MAC IC 13. The modulated signal is amplified by the individual RFIC 12 to have a higher frequency. The high-frequency signal is then transmitted to the air via the antennas 15. In such manner, the data transmission rates in receiving/transmitting modes are increased.
For a purpose of enhancing capability of wireless communication and data transmission rates, a multiple-input multiple-output (MIMO) system is integrated into notebook computers. Generally, the antennas for supporting the MIMO system are disposed at different locations around the liquid crystal display panel of the notebook computer. In a case that three antennas are employed, the first one may be disposed at upper portion of the liquid crystal display panel, while the other two antennas are disposed at bilateral sides of the liquid crystal display panel. The operational settings of the WLAN module are dependent on the distance between the individual antenna and the RF connector. However, if the size of the liquid crystal display panel is changed, the operational settings of the WLAN module should be varied as well.